The exponential growth in the demand of wireless data communications has put a tremendous pressure on the cellular network operators to improve the capacity of their communication networks. To improve the spectral efficiency of these networks, scarce radio resources have to be reused aggressively in neighboring cells. As a result, inter-cell interference (ICI) has become a main source of signal disturbance, limiting not only the service quality of the cell-edge users, but also the overall system throughput.
Coordinated multi-point (CoMP) transmission or reception is one known means to effectively mitigate inter-cell interference. In CoMP systems, a central processor coordinates downlink transmissions to, and possibly also uplink transmissions from, all users in the cells forming the CoMP system. The central processor transmits to each base station—via a backhaul data communication network—a representation of the RF signal to be transmitted into its cell by each antenna. The central processor coordinates and optimizes transmissions to reduce or even avoid mutual interference among users.
Downlink CoMP transmission systems, in particular, can effectively mitigate ICI using multi-user precoding techniques. Multi-user precoding allows simultaneous transmission over the same frequency band to multiple users without creating any mutual interference (within a CoMP cluster 10) by sending signal to each user in a “direction” orthogonal to the channel and other users. However, the amount of information the central processor is required to send to or receive from each remote base station can be overwhelming, particularly when multiple antennas are deployed at each base station. The antenna signals to be distributed, in general, are complex-valued downlink signals comprising both In-phase (I) and Quadrature (Q) components for each antenna branch. In the standard Common Public Radio Interface (CPRI), each real-valued sample of the IQ backhaul signal would simply be quantized independently by a fixed number of bits (e.g., 16), without considering any structure of the underlying backhaul signal. The sheer quantity of such transmission places a large burden on the capacity of backhaul links—indeed, the capacity of backhaul communication links between the central processor and multiple base stations may limit CoMP system 10 performance.